1. Field
The present disclosure relates to an operation method of a fuel cell system and a fuel cell system.
2. Description of the Related Art
In a fuel cell, hydrogen is supplied as fuel gas to an anode and air is supplied as oxidant gas to a cathode, hydrogen ions generated at the anode by a catalytic reaction move through an electrolyte membrane to the cathode, and have an electrochemical reaction with oxygen in the air to generate electricity at the cathode.
A fuel cell system includes an anode-side passage through which fuel gas is circulated in the fuel cell, and a cathode-side passage through which oxidant gas is circulated in the fuel cell. The cathode-side passage may be provided with a bypass passage (branch passage) that dilutes hydrogen of oxidant off-gas and controls the pressure in the cathode-side passage (see, for instance, Japanese Unexamined Patent Application Publication No. 2004-172027 and Japanese Unexamined Patent Application Publication No. 6-111840).
It is known that when the electrolyte membrane of a fuel cell is in an excessively dried state (hereinafter referred to as “dry-up state”), the power generation performance of the fuel cell is reduced, and eventually resulting in deterioration of the electrolyte membrane. Therefore, in the fuel cell system, dry-up state is avoided by appropriately controlling a flow rate of the oxidant gas that flows within the cathode-side passage, according to the power generation amount of the fuel cell.
In addition, the fuel cell system is provided with a pump for circulating the oxidant gas through the cathode-side passage. Various types of pump are adopted as the pump, such as what is called a Lysholm pump and a turbo pump. In the case of a Lysholm pump, it is possible to easily control a flow rate of the oxidant gas that flows within the cathode-side passage, according to the power generation amount of the fuel cell.